327 / 4 BBL Intake - Carb Recommendations & Exhaust Crossover Question

[Harry Dawg]

Hello Friends.
After scouring the internet, I was finally able to track down a 4 BBL intake off a 66' AMC Marlin for my 68' Gladiator.
Such a cool community that AMC fans have developed over the years, and it was honestly fun to track this thing down.
Anyways, I have a couple of questions about this swap.
1) What is the exhaust crossover? I have heard of folks blocking this off, and I would imagine that you would need to in order to run any carb without a hot air choke? Thoughts on this?
2) Anyone have any carb recommendations. What CFM should I be looking for? I was thinking no more than 600 CFM, with 400-500 being ideal.
Can anyone explain the science behind determining CFM, Exhaust to intake ratio etc.?
P.S. I know there is a thread about this somewhere else on the forum, but I didn't really find the information I was looking for.
Thanks!

[Stuka]

The main purpose of the exhaust crossover is to provide better drivability by warming the plenum of the intake to provide better atomization. If it gets too cool, the fuel can condense on the inside of the intake and cause rich/lean states across the cylinders. There is no reason to block it off for a street car. For race only applications where drivability isn't a concern, its fine to do. And many after market intakes do not have it at all. It does make the engine much more cold blooded. And testing has shown a negligible impact on performance.

For carb size, you can use a site like here: https://www.inchcalculator.com/carburet ... ciency=.85

Its important to use one that takes VE (volumetric efficiency) into account. I would be surprised if that engine is much over 80%. 400cfm sounds about right for it. Holley makes a 400CFM 4v.

If you are going to drive it almost all on the street, a regular holley/edelbrock will be fine. If you want to do some offroading, even if mild, I would go with the 470cfm Truck Avenger.

[tgreese]

Holley also makes a 390CFM 4160 4V which I'd think would be a good size for this engine. The 327 is a first-generation V8 with less sophisticated breathing, and I'd think any larger carb would not demonstrate a performance advantage. Plus a too-big carb must be set up rich to be driveable... not what you want.

Apparently some Jeeps with this engine came with a 4V Holley, of the 4160 style. These carbs are not known for trail performance, but you can tinker with them and add some features to make them perform better over bouncy terrain and at odd angles. Look online for more discussion.

https://www.holley.com/products/fuel_sy ... rts/0-8007

The 470TA will be better for trail use without any mods, but supposedly it can have responsiveness issues on the street. Search old posts here and at IFSJA and you'll find plenty of discussion.

[Harry Dawg]

Thanks for the explanation of the exhaust crossover Stuka. I believe I will just leave it alone given that information.
I just figured it was odd that burnt exhaust gases were being added back into the fuel air mixture.
Seems like it would decrease available oxygen creating a richer blend, but what do I know!
As for the carbs, I appreciate the recommendations, but some of these are upwards of $700.
I would probably go with the Sniper setup at that price point.
Any suggestions on something I could pickup on market place, or at a swap meet?
I was thinking about a Motocraft 4300 (441 CFM)
The only reason I decided to swap the intake was so I could have more carb options, but it seems like the 4BBL intake only slightly opened up my options.
I know power gains will be negligible, but I didn't want to fool around with the Holley 2209 that came factory.

[tgreese]

There's also a 4100 Motorcraft carb that was used on Fords for many years. AFAIK it's a good carburetor, perhaps better than the 4300. The 4300 was used '73-74 for the 360 4V, so you might find one from a Jeep enthusiast. Or a used Holley. Holleys have the advantage in tuning parts and flexibility that the Motorcrafts do not.

Rochester Quadrajets have small primaries and can work very well, but you'd need to adapt it to your manifold. Plus they have a reputation for being complicated, but I suspect that depends on how much study about tuning you're willing to invest.

[Harry Dawg]

Intake

[Harry Dawg]

Before cleaning

[Harry Dawg]

As always Tgreese, thanks for your input.
I believe I will start the hunt for a 4100. Looks to be in my price range, and seems to be the basic, bare bones carb I have been looking for.
If you remember a couple of months ago, you helped me identify the Holley 2209 on this unit.
I was wanting to swap the carb to the MC2100 from the start, but the factory intake wouldn't allow it.
Ideally I would have kept it a 2 barrel, but at least I have the option to swap something....anything on there besides the factory Holley.
Here are some pics of the factory intake and valley pan if any anyone is interested to see what I have been working on.
Thanks again for everyone's feedback.

[Harry Dawg]

After cleaning

[tgreese]

NP. Glad to help.

I had a passenger car 352 in my '65 F100, and it had a 4100 from the factory. It worked fine, except the carburetor body was worn out around the throttle plate shaft. This would leak air and not idle consistently. I found a junkyard Holley 4160 to replace it, which worked well.

[Harry Dawg]

Update on the carb hunt. I was able to find a pretty decent 4100 for only $30 bucks.
The rebuild kit was actually more than the carb itself!
Got the rebuild from Mike's Carburetor Parts in Washington State. https://www.carburetor-parts.com/
He puts YouTube videos up on how to rebuild, and includes a free PDF of the carb's manual with purchase of a rebuild kit.Happy to support his business.
Here are some pictures of the carburetor. I wish it had the ID tag so I can determine what this came off of. The only markings on this thing are EDC and RA2.... I know we are getting into Ford territory here, so let me get back on track.

Some general thoughts on carburetor theory here.

The 1965 352 Galaxie produced 300 HP at 4,600 RPM ( I am guessing that is max RPM).
This would be roughly the same max RPM as my 327 makes based on Stuka's feedback.
The reason I bring this up is to better understand general theory here.
I am guessing that since both have similar displacement and max RPM ranges, the 4100 should be a good fit for my engine.
The question is, what would have been the advantage over the 2 barrel? There was a factory option for a 4 barrel carb on this AMC 327, so I am just kind of wondering about different engine/carb configurations. The 4100 looks massive compared to my factory 2 barrel, but the CFM shouldn't be too much for my application based on the the above reasoning. Was the 2 barrel just to save on fuel?

Next up on my questionare is jet size. These carbs came with several jets based on what vehicle this was going on.
Let's say this carb came from a police special T-bird with the 428 engine (1/2" primary, 5/8" secondary) . Could I just swap in jets meant for a 289 cu Mustang ( 1/2" primary, 17/32" secondary) to better fine tune the carb for my truck?
The measure on the primary is the same for both motors, but I can't imagine that the 428 and 289 would require the same amount of fuel?

I know that this isn't FSJ tech, so feel free to delete if not allowed.

[Harry Dawg]

Side Shot

[Harry Dawg]

Side by Side

[tgreese]

That's a 4100 alright.

I would expect it to have the venturi diameter cast into the side, like the 2100.

Did it come with the choke gear that's missing from the near side?

You could clean it up and run it, and see how it goes. There's not a lot to adjust - you can change the jets, change the pump shot (some - limited by the arm settings), change the power valve. As I mentioned, the QUickFuel power valves are said to fit the Autolite/Motorcraft carbs. Holley has a tech note on their site about picking the right power valve.

[Harry Dawg]

Yes.
It came with an automatic (thermostat style w/ clock spring) choke. You can see it in the back with the little yellow zip ties.
It also came with an insulator/spacer with a large vacuum port. TBD what that will hook up too and a new gasket.
I purchased the master rebuild kit with new floats, secondary diaphragm, hardware, vent tubes etc., so hopefully it will have anything that is missing in it.

I believe the venturi size may be stamped on the underside of each venturi, but I haven't gotten that far into it yet.

[tgreese]

Venturi size on the 2100 - suspect 4100 is similar:

2100VenturiSize (1000 x 562).jpg

1.21"

There is a plastic piece that's threaded and fits into the end of the choke arm, where what appears to be a cotter key is now. I found that online for repair of a 2100 maybe a decade ago - search might turn it up.

Port in the insulator is for PCV. I'd guess that's an old carburetor, ca 1960ish? Bowl vent on the top of the primary bowl that's low and always open is another anachronism.

[tgreese]

I'll just put this here -

https://www.ebay.com/itm/265509590626?e ... SwreVh6N0l

These Holleys are made to be tuned to your application. You can buy maybe a dozen different books on Amazon or Alibris about how to tune a Holley. Speed shops (online or brick-and-mortar) have all the tuning parts, and the bits you need to make them work well on the trail (spring loaded needle, vent whistle, etc.) Raise the bowl vents - look at the 470TA.

Not berating your 4100, but you'd be starting with a lot more potential if you had an 8007 like this.

[Harry Dawg]

So I ended up not using the Autolite 4100. I really wanted to give it a shot but the carb was just too far gone. Ended up going with a QFT- 450 CFM Slayer Series. The adjustable vacuum secondary, four corner adjustment and sight glasses were a big selling point for me, and the CFM was only 25 more than the calculator projected it should be. $400 was a little more than I wanted to spend, but at least I won't have to fool with it and I'll have a good, if not great carb. Still need to run fuel line, so I will update when I get her fired up.
I also plan to run a carb spacer to keep the heat from the cross over down.

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[Harry Dawg]

Ended up needing a different throttle cable bracket. This one off Amazon works good.

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[Brly]

Well, how does it run?